Various techniques are known in the art for sealing joints in the manufacture of packaging containers. In those cases where the packaging material includes a conductive layer, for example aluminium foil, and a heat fusing medium, for example, a thermoplastic layer, induction heat sealing may be employed for sealing a joint.
U.S. Pat. No. 5,889,263 describes, for example, an apparatus for induction sealing of a packaging material which includes a layer of aluminium foil. The apparatus comprises an inductor with two parallel conductors interconnected by two transverse conductors. The parallel conductors are disposed in an electrically insulated carrier portion. The transverse conductors are disposed in the upper surface of the inductor and coincide with the outer edges of a flat-laid tube of packaging material. The inductor is enclosed in a sealing jaw which is disposed to urge a double layer of the packaging material against a counter jaw. The parallel conductors are connected to a current source, an induction current being generated in the layer of aluminium foil. Heat is generated and each one of the conductors forms a seal of the packaging material. Between these two seals, the packaging material can be cut. With the aid of this apparatus, a seal for each one of two packages may thus be formed at the same time. The apparatus is restricted to the sealing of joints between mutually united and compressed layers of the packaging material, i.e. for transverse sealing of a flat-laid tube of packaging material.
WO2003SE01793 describes another type of packaging container where induction thermosealing is employed. This packaging container consists of a first and second packaging part which are sealed to one another. The first part is tubular and has been manufactured from a sheet of thermoplastically coated packaging material which includes at least one layer of aluminium foil. The sheet has a sealed first overlap joint between two mutually opposing edge sections of the sheet. The second part, which consists of a plastic top with an opening arrangement, is sealed to the first part by means of a second overlap joint. At one point in the packaging container, the two overlap seals intersect one another.
Further developments of this latter described packaging container have proved that it may be further improved.